1. Field of the Invention
The present invention relates to a flaw detecting apparatus for conducting non-destructive flaw inspection for axles, such as an axle of electric railcars.
2. Related Arts
FIG. 1 is a schematic diagram showing the structure of an axle ultrasonic flaw detecting apparatus of the prior art. In this figure, the reference numeral 1 designates an axle of an electric railcar as an inspected object; 3a, 3b drivers for moving and shifting probe heads 2a, 2b in mutually vertical three directions; 4 an ultrasonic flaw detector which is provided to cause the probe heads 2a, 2b to transmit an ultrasonic wave and receive echoes inputted to the probes 2a, 2b; 5 a display unit for displaying the output of the ultrasonic flaw detector 4; 6 an oil feeding unit for filling a gap between the probe heads 2a, 2b and the end faces of the axle 1 with oil; 7 an operation controller for outputting operation instructions to the drivers 3a, 3b and oil feeding unit 6.
FIGS. 2(a) and 2(b) show an enlarged view of an end of the axle 1 of an electric railcar, more specifically FIG. 2(a) is a side elevation of the axle 1, while FIG. 2(b) is a plan view of one end face of the axle 1. In these figures, N.sub.0 designated a center hole for positioning a wheel lathe used to cut a wheel at its center and N.sub.1, N.sub.2, N.sub.3 threaded holes which receive bosses for mounting the wheel to the axle 1 and which are arranged at an angular interval of 120.degree.; and N.sub.4 a marking for indicating a wheel number.
When a switch of the operation controller 7 for moving the probe head 2a in a first direction is depressed in order to set the probe head 2a in contact with one end face of the axle 1, a control signal is sent to the driver 3a from the operation controller 7 and the probe head 2a is moved in the first direction by the driver 3a. Similar to the moving in the first direction, the probe head 2a can also be moved in the second and third directions by the driver 3a in response to the depression of the 2nd and 3rd direction buttons provided on the operation controller 7. Upon completion of the operations explained above, the probe head 2a comes into contact with the center of one end face of the axle 1. The probe head 2b can also come in contact with the center of the other end face of the axle 1 in the same manner as mentioned above. After the probe heads 2a, 2b have come in contact with the centers of both end faces of the axle 1, oil is instructed to be fed by the operation controller 7. When an instruction to feed oil is issued, a control signal is sent to the oil feeding unit 6 from the operation controller 7 and the gaps between the end faces of the axle 1 and the probe heads 2a, 2b are respectively filled with oil. Next, the ultrasonic flaw detector 4 is operated to transmit an ultrasonic wave from a probe built in the probe head 2a and echoes are received by the probe built in the probe head 2a and then transmitted through the ultrasonic flaw detector 4 to the display 5 which displays the echoes as shown in FIGS. 3(a) and 3(b).
FIG. 3(a) shows a typical waveform in the case the axle 1 does not contain any flaw, while FIG. 3(b) shows a typical waveform in the case flaws exist inside the axle 1. In those figures, S designates a surface echo; B a bottom echo; F a flaw echo and H a step echo.
Next, when a switch of the operation controller 7 for rotating the probe head 2a is depressed, a control signal is sent to the driver 3a from the operation controller 7 and the driver 3a rotates the probe head 2a. During the rotation of the head 2a, an operator monitors waveforms displayed on the display 5 and stops the rotation of the probe head 2a by operating the operation controller 7 when a flaw waveform as shown in FIG. 3(b) which is different from a standard waveform shown in FIG. 3(a) appears. When the probe head 2a stops, the amplitude of each echo is evaluated to determine whether it should be considered to emanate from a flaw or not on the basis of a waveform displayed on the display 5. When an echo is determined to be generated by a flaw, the distance from one end face of the axle 1 to the flaw is obtained using the waveform on the display 5 and is then recorded. A circumferential position of the flaw is also recorded as an angular position relative to the threaded hole N.sub.2 located in the right of the marking N.sub.4 shown in FIG. 2(b).
When the probe head 2a passes over the threaded holes N.sub.1, N.sub.2 and N.sub.3 formed on one end face of the axle 1, a displayed waveform is disturbed and flaw detection is not carried out for such regions.
Using the driver 3b and probe head 2b, flaw detection is also carried out for the other end face of the axle 1.
Since a flaw detecting apparatus of the prior art is constituted such as explained above, an operator is required to manually position a probe head so that it comes into contact with the center of an end face of an axle. This gives rise to a problem that a positioning accuracy considerably fluctuates and that a long time is required for such positioning.
Moreover, since a result of flaw detection is visually judged in addition to manually positioning a probe head, reproducibility in the result of flaw detection may be compromised if the same axle is Inspected a plurality of times. Visual judgment also results in a drawback that a skilled operator is essential.